IL4 and periodontitis: To reverse the inflammatory environment and promote tissue regeneration for periodontitis in terms of the mechanical aspect, He et al. developed a high-stiffness and injectable transglutaminase crosslinked gelatin hydrogel (TG-gel) with the encapsulation of M2-inducing immunomodulatory interleukin-4 (IL-4) and stem cell-chemoattractant stromal cell-derived factor-1α (SDF-1α) as an artificial environment for modulating immune cells, and homing the stem cells for in situ regeneration to repair periodontal defects [131].